(1) Field of the Invention
This invention relates to the casting of metal strip articles by means of continuous strip casting apparatus of the kind that employs continuously moving elongated casting surfaces. More particularly, the invention relates to a method of and apparatus for measuring variations of the separation of such surfaces within the casting region of the apparatus.
(2) Description of the Related Art
Metal strip articles (such as metal strip, slab and plate), particularly those made of aluminum and aluminum alloys, are commonly produced in continuous strip casting apparatus. In such apparatus, molten metal is introduced between two closely spaced (usually actively cooled) elongated moving casting surfaces forming a narrow casting cavity. The metal is confined within the casting cavity until the metal solidifies (at least sufficiently to form an outer solid shell), and the solidified strip article is continuously ejected from the casting cavity at an exit by the moving casting surfaces and may be produced in indefinite length. One form of such apparatus is a twin-belt caster in which two confronting belts are circulated continuously and molten metal is introduced between the belts by means of a launder or injector into a thin casting cavity formed between the confronting regions of the belts. An alternative is a rotating block caster in which the casting surfaces are formed by blocks that rotate around a fixed path and join together adjacent the casting cavity to form a continuous surface. The metal is conveyed by the moving belts or blocks for a distance effective to solidify the metal, and then the solidified strip emerges from between the blocks at the opposite end of the apparatus.
It is desirable to make the casting surfaces as flat as possible, even though these surfaces may be made to converge, diverge or run parallel to each other, according to the dictates of particular casting procedures and conditions. When the surfaces are not flat, heat extraction from the metal being cast and application of force vary unpredictably and the resulting cast slab may show surface and/or internal defects. Variations of the casting surface from planar may result from distortions or displacements of the elements that form the casting surfaces caused by such things as welds used to construct the elements, exposure to heat and flexing and/or from distortions of underlying supports used to guide the moving elements. For example, in the case of belt casting apparatus, the reverse surfaces of the belts are generally supported on and slide over surfaces made up of numerous flat closely packed stationary nozzles that may diverge from a planar orientation with each other and may also individually twist out of the intended orientation, especially as they are used to deliver a stream of cooling water to the reverse surfaces of the belts.
While it is possible to remove the casting belts from the casting apparatus to subject them and their supports to checks for flatness, this is labor-intensive and requires the apparatus to be cooled and the supply of cooling water to be terminated. It would be advantageous to be able to check for deviations from flatness with the casting elements in place and the water supply in operation, as this would give results more in keeping with actual casting conditions. However, the nature of the casting cavity (being relatively thin but of considerable length and breadth) makes this difficult, as does the fact that the apparatus may be quite hot if it has already been used for previous casting operations.
U.S. Pat. No. 4,294,305 issued to Oda on Oct. 13, 1981 discloses a device for measuring a gap between a plurality of roll pairs designed to guide and bend a steel ingot around a radius after it exits a vertically-positioned mold. However, the patent is not concerned with measuring a casting cavity.
U.S. Pat. No. 3,937,270 to Hazelett et al. issued on Feb. 10, 1976 uses an array of fixed mechanical and thermal probes arranged on the reverse side of belts used to form a casting cavity. The mechanical probes contact the belts directly and measure transverse buckling. However, the casting cavity is not measured directly.
U.S. Pat. No. 5,086,827 to Graham et al. issued on Feb. 11, 1992 discloses the use of one or more fixed non-contact sensors for measuring belt flatness in a twin belt casting apparatus. As in the Hazelett et al. reference mentioned above, the sensors are positioned at the reverse surfaces of the belts and do not measure the separation and flatness of the surfaces forming the casting cavity itself.
There is therefore a need for a method and apparatus for directly measuring the spacing and flatness of surfaces forming a casting cavity for strip article casting.